Chemical Separation and Isotopic Variations of Cu and Zn From Five Geological Reference Materials

This paper presents an adapted anion exchange column chemistry protocol which allowed separation of high-purity fractions of Cu and Zn from geological materials. Isobaric and non-spectral interferences were virtually eliminated for consequent multiple-collector ICP-MS analysis of the isotopic composition of these metals. The procedure achieved ∼ 100% recoveries, thus ensuring the absence of column-induced isotopic fractionation. By employing these techniques, we report isotopic analyses for Cu and Zn from five geological reference materials: BCR-027 blende ore (BCR), δ⁶⁵Cu = 0.52 ± 0.15‰ (n = 10) and δ⁶⁶Zn = 0.33 ± 0.07‰ (n = 8); BCR-030 calcined calamine ore (BCR), δ⁶⁶Zn = -0.06 ± 0.09‰ (n = 8); BCR-1 basalt (USGS), δ⁶⁶Zn = 0.29 ± 0.12‰ (n = 8); NOD-P-1 manganese nodule (USGS), δ⁶⁵Cu = 0.46 ± 0.08‰ (n = 10) and δ⁶⁶Zn = 0.78 ± 0.09‰ (n = 9); SU-1 Cu-Co ore (CCRMP), δ⁶⁵Cu = -0.018 ± 0.08‰ (n = 10) and δ⁶⁶Zn = 0.13 ± 0.17‰ (n = 6). All uncertainties are ± 2s; copper isotope ratios are reported relative to NIST SRM-976, and zinc isotope ratios relative to the Lyon-group Johnson Matthey metal (batch 3-0749 L) solution, JMC Zn. These values agree well with the limited data previously published, and with results reported for similar natural sample types. Samples were measured using a GVi IsoProbe MC-ICP-MS, based at the Natural History Museum, London. Long-term measurement reproducibility has been assessed by repeat analyses of both single element and complex matrix samples, and was commonly better than ± 0.07‰ for both δ⁶⁶Zn and δ⁶⁵Cu.     

Deep Gemini/GMOS imaging of an extremely isolated globular cluster in the Local Group

We report on deep imaging of a remote M31 globular cluster, MGC1, obtained with Gemini/GMOS. Our colour–magnitude diagram for this object extends ∼5 mag below the tip of the red-giant branch and exhibits features consistent with an ancient metal-poor stellar population, including a long, well-populated horizontal branch. The red-giant branch locus suggests MGC1 has a metal abundance  [M/H]≈−2.3  . We measure the distance to MGC1 and find that it lies ∼160 kpc in front of M31 with a distance modulus  μ= 23.95 ± 0.06  . Combined with its large projected separation of   R _p= 117 kpc  from M31, this implies a deprojected radius of   R _gc= 200 ± 20 kpc  , rendering it the most isolated known globular cluster in the Local Group by some considerable margin. We construct a radial brightness profile for MGC1 and show that it is both centrally compact and rather luminous, with   M_V =−9.2  . Remarkably, the cluster profile shows no evidence for a tidal limit and we are able to trace it to a radius of at least 450 pc, and possibly as far as ∼900 pc. The profile exhibits a power-law fall-off with exponent  γ=−2.5  , breaking to  γ=−3.5  in its outermost parts. This core-halo structure is broadly consistent with expectations derived from numerical models, and suggests that MGC1 has spent many gigayears in isolation.     

Global geographic differences in marine metals toxicity

Biochemical reaction rates, metabolic rates, and other rates of biological activity increase exponentially with temperature. It has thus been hypothesized that toxicity to chemical contaminants may increase from polar to temperate to tropical species; however, until recently, polar data to test this hypothesis were not available. This study examined differences in the acute sensitivities of marine invertebrates to four metals (Cu, Cd, Zn, Pb) for polar, temperate and tropical species; data deficiencies for polar regions prohibited comparisons using chronic end-points or other chemicals. Differences between the three geographic regions were not predictable based on temperature (other factors such as differences in dissolved organic carbon concentrations also affect toxicity). There appears to be no universal, predictable pattern of increased toxicity from polar to tropical regions. Toxicity data from one geographic region will not be universally protective of other regions.     

Cyanopolyynes in hot cores: modelling G305.2+0.2

We present results from a time-dependent gas-phase chemical model of a hot core based on the physical conditions of G305.2+0.2. While the cyanopolyyne HC₃N has been observed in hot cores, the longer chained species, HC₅N, HC₇N and HC₉N, have not been considered as the typical hot-core species. We present results which show that these species can be formed under hot core conditions. We discuss the important chemical reactions in this process and, in particular, show that their abundances are linked to the parent species acetylene which is evaporated from icy grain mantles. The cyanopolyynes show promise as 'chemical clocks' which may aid future observations in determining the age of hot core sources. The abundance of the larger cyanopolyynes increases and decreases over relatively short time-scales,  ∼10^2.5 yr  . We present results from a non-local thermodynamic equilibrium statistical equilibrium excitation model as a series of density, temperature and column density dependent contour plots which show both the line intensities and several line ratios. These aid in the interpretation of spectral-line data, even when there is limited line information available. In particular, non-detections of HC₅N and HC₇N in Walsh et al. are analysed and discussed.     

Submillimetre detection of the z=2.83 Lyman-break galaxy, Westphal–MM8, and implications for SCUBA2

We present confusion-limited submillimetre (submm) observations with the Submillimetre Common-User Bolometer Array (SCUBA) camera on the James Clerk Maxwell Telescope of the   z = 2.83  Lyman-break galaxy (LBG), Westphal–MM8, reaching an 850 μm sensitivity even greater than that achieved in the SCUBA map of the Hubble Deep Field region. The detection of MM8  ( S _850 μm= 1.98 ± 0.48 mJy)  , along with the literature submm detections of lensed LBGs, suggests that the LBG population may contribute significantly to the source counts of submm-selected galaxies in the 1–2 mJy regime. Additionally, submm-luminous LBGs are a viable progenitor population for the recently discovered evolved galaxies at   z ∼ 2–2.5  . These observations represent an important baseline for SCUBA2 observations which will regularly map large regions of the sky to this depth.     

Episodes of floods in Mangala Valles,Mars, from the analysis of HRSC,MOC and THEMIS images

The Mangala Valles is a 900-km long outflow channel system in the highlands adjacent to the south-eastern flank of the Tharsis bulge. This work was intended to answer the following two questions unresolved in previous studies: (1) Was there only one source of water (Mangala Fossa at the valley head which is one of the Medusae Fossae troughs or graben) or were other sources also involved in the valley-carving water supply, and (2) Was there only one episode of flooding (maybe with phases) or were there several episodes significantly separated in time. The geologic analysis of HRSC image 0286 and mapping supported by analysis of MOC and THEMIS images show that Mangala Valles was carved by water released from several sources. The major source was Mangala Fossa, which probably formed in response to magmatic dike intrusion. The graben cracked the cryosphere and permitted the release of groundwater held under hydrostatic pressure. This major source was augmented by a few smaller-scale sources at localities in (1) two mapped heads of magmatic dikes, (2) heads of two clusters of sinuous channels, and (3) probably several large knob terrain locals. The analysis of results of crater counts at more than 60 localities showed that the first episode of formation of Mangala Valles occurred ～3.5 Ga ago and was followed by three more episodes, one occurred ～1 Ga ago, another one ～0.5 Ga ago, and the last one ～0.2 Ga ago. East of the mapped area there are extended and thick lava flows whose source may be the eastern continuation of the Mangala source graben. Crater counts in 10 localities on these lava flows correlate with those taken on the Mangala valley elements supporting the idea that the valley head graben was caused by dike intrusions. Our observations suggest that the waning stage of the latest flooding episode (～0.2 Ga ago) led to the formation at the valley head of meander-like features sharing some characteristics with meanders of terrestrial rivers. If this analogy is correct this could suggest a short episode of global warming in Late Amazonian time.     

Revealing the transition from post-AGB stars to planetary nebulae: non-thermal and thermal radio continuum observations

Midcourse Space eXperiment and Infrared Astronomical Satellite colour diagnostics as well as OH maser profile characteristics were used to select a sample of post-asymptotic giant branch (pAGB) candidates for a radio continuum detection experiment with the Australia Telescope Compact Array. Seven out of 28 sources, six of which are new detections, show a continuum. A planetary nebula serendipitously detected in the field of an undetected pAGB candidate also reveals radio continuum. The radio continuum properties of these eight sources are described. Almost half have non-thermal emission. dusty modelling of the infrared spectral energy distributions (SEDs) of the three strongest detections reveals that they all have central stars with temperatures substantially lower than that required for significant photoionization, leading us to infer that the radio continuum has arisen from wind–shock interactions. This hypothesis is consistent with the detection of non-thermal radio emission in one of these three objects.     

Iron isotope fractionation during leaching of granite and basalt by hydrochloric and oxalic acids

Transport of iron (Fe) within hydrothermal and soil environments involves the transferral into aqueous solutions by leaching of complex, polyminerallic rocks. Understanding the isotope fractionation mechanisms during this process is key for any application of the Fe-isotope system to biogeochemical studies. Here, we reacted biotite granite and tholeiite-basalt with 0.5 M hydrochloric acid and 5 mM oxalic acid solutions at ambient temperature. Solution aliquots were recovered over a seven-day period and analysed for major and trace element concentrations and Fe isotopic compositions. In all experiments, Fe initially released into solution was isotopically lighter, with Δ⁵⁶Fe_{solution-rock} as low as −1.80‰ in the granite-hydrochloric acid system. The oxalic acid experiments showed similar patterns but smaller fractionation. In all experiments, the Δ⁵⁶Fe_{solution-rock} reduced over time, which would be in line with the formation of a leached layer as proposed before [Brantley S. L., Liermann L. J., Guynn R. L., Anbar A., Icopini G. A., and Barling J. (2004) Fe isotopic fractionation during mineral dissolution with and without bacteria. Geochim. Cosmochim. Acta68(15), 3189-3204]. Granite and basalts reacting with hydrochloric acid reached apparent steady-state values of −0.60 ± 0.15‰ and −0.40 ± 0.20‰, respectively, whilst experimental values with oxalic acid were −1.0 ± 0.15‰ and −0.50 ± 0.15‰. During the granite experiments, alteration of biotite to chlorite, followed by dissolution of chlorite, were likely the dominant processes, whilst in the basalt experiments, dissolution of pigeonite was likely the principal source of Fe. Variations in pH during the hydrochloric acid experiments were minimal, remaining below 0.5 at all times. In oxalic acid solutions, the pH increased to over 4, leading likely to precipitation of secondary minerals and adsorption/co-precipitation of Fe onto mineral surfaces. These processes could contribute to the greater fractionation observed in the final stages of the oxalic acid experiments. Our results highlight the importance of mineralogy and fluid composition on the Fe-isotope systematics during weathering. The fractionation processes identified for granites and basalts are in line with those inferred from field observations in soils, sediments, groundwater and hydrothermal deposits and from laboratory studies of single-mineral leaching.     

Modelling of rail surface temperatures: a preliminary study

Summary Variations in rail temperature are responsible for a large proportion of weather related delays on the rail network. Tracks are pre-stressed to withstand a specified range of temperature, but once the range is breached the rail can distort causing tension cracks in cold weather and buckling in hot weather. Currently, blanket speed restrictions are imposed at certain temperature thresholds to ensure passenger safety. This paper discusses the measurement and modelling of rail temperature data at both a specially constructed test track and a ‘live’ main-line track. Although, empirical techniques are presently used to derive rail temperatures from air temperatures, this approach is limited as it fails to take into account other ambient weather conditions. To address this, a road weather model was converted to model the energy balance of a rail. This enables rail temperatures to be forecasted for the entire diurnal cycle and at a variety of synoptic conditions. The physical model shows significant forecasting ability, outperforming empirical techniques with a mean bias of 0.2 °C (RMSE = 2.56°) for a 200 day measurement campaign. Authors’ address: L. Chapman, J. E. Thornes, Y. Huang, X. Cai, V. L. Sanderson, S. P. White, Entice Technology Ltd, School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, U.K.